Technically it's already possible, many websites already implement it.
The problem is majority of internet users don't have Bitcoin or a lightning wallet.
And because of that, the majority of websites arent using paywalls.
Discussion
So from a social/behavior standpoint, I suppose something like a browser extension wallet that could be easily topped up and seamlessly send sats as sites are accessed?
For most users, custodial is easier. Then fiat to sat conversions like #[4] is doing. Maybe?